WIRELESS AND MOBILE COMMUNICATION RADIO AND SATELLITE COMMUNICATION

WIRELESS AND MOBILE COMMUNICATION RADIO AND SATELLITE COMMUNICATION 1 Lecture-5 Instructor : Mazhar Hussain

TYPES OF WIRELESS COMMUNICATION celullar wireless computer network radio service 2

RADIO COMMUNICATION Radio or radio communication means any transmission, emission, or reception of signs, signals, writing, images, sounds or intelligence of any nature by means of electromagnetic waves of frequencies lower than three thousand gigacycles per second (3000 GHz) propagated in space without artificial guide. Examples of radio communication systems: Radio broadcasting. TV broadcasting. Satellite communication. Mobile Cellular Telephony. Wireless LAN. Multimedia communication & Mobile Internet 3 [Slimane]

HISTORY 1864: Maxwell describes radio wave mathematically 1888: Hertz generates radio waves 1890: Detection of radio waves 1896: Marconi makes the first radio transmission 1915: Radio tubes are invented 1948: Shannon’s law 1948: Transistor 1960: Communication Satellites 1981: Cellular technology 4

CLASSIFICATION OF RADIO SPECTRUM AM broadcasting, naviation, radio beacons, distress frequencies. Broadcasting TV, satelites, Personal telephone systems, radar systems, fixed and mobile satelite services Fixed services, Fixed statelite services, Mobile serivces, Remote sensing Frequency assaignments up 60 GHz 300 -3000 Hz 3 -30 k. Hz 30 -300 k. Hz 300 -3000 KHz 3 -30 MHz 30 -300 MHz 300 -3000 MHz 3 -30 GHz 30 -300 GHz Wavelength 1000 -100 km 100 -10 km 10 -1 km 1000 -100 m 100 -10 m 10 -1 m 100 -10 cm 10 -1 mm Term ELF VLF LF MF HF VHF UHF SHF EHF Time and Frequency Normals, Navigation, Underwater Communication, Remote sensing under ground, Maritme telegraphy Broadcasting, TV, FM, Mobile services for maritime, aeronautical and land, Wireless microphones, Meteor burst communicaiton Fixed point to point communication, Mobile maritime aeronautical, land services, military communication, amateur radio and broadcasting Long distance communication (fixed and marite), Broadcasting, Naviagation, Radio beacons Frequency Application 5

EVOLUTION OF WIRELESS SYSTEMS 6 [Stallings. , 2005]

RADIO COMMUNICATION Three main problems: The path loss Noise Sharing the radio spectrum 7

TYPES OF ELECTROMAGNETIC CARRIERS when the distance between the sender and receiver is short (e. g. TV box and a remote control) infrared waves are used for long range distances between sender and receiver (e. g. TV broadcasting and cellular service) both microwaves and radio waves are used radio waves are ideal when large areas need to be coverd and obstacles exist in the transmission path microwaves are good when large areas need to be coverd and no obstacles exist in the transmission path 8

WIRELESS APPLICATIONS (SERVICES) 9

ADVANTAGES AND DISADVANTAGES OF WIRELESS COMMUNICATION advantages: mobility a wireless communication network is a solution in areas where cables are impossible to install (e. g. hazardous areas, long distances etc. ) easier to maintain disadvantages: has security vulnerabilities high costs for setting the infrastructure unlike wired comm. , wireless comm. is influenced by physical obstructions, climatic conditions, interference from other 10 wireless devices

FREQUENCY CARRIES/CHANNELS The information from sender to receiver is carrier over a well defined frequency band. This is called a channel Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate) Different frequency bands (channels) can be used to transmit information in parallel and independently. 11

BASICS OF RADIO COMMUNICATION 12

RADIO WAVES GENERATION when a high-frequency alternating current (AC) passes through a copper conductor it generates radio waves which are propagated into the air using an antena radio waves have frequencies between: 3 Hz – 300 KHz - low frequency 300 KHz – 30 MHz – high frequency 30 MHz – 300 MHz – very high frequency 300 MHz – 300 GHz – ultra high frequency 13

BASICS: HOW DO SATELLITES WORK Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a satellite as a relay station for their communication One Earth Station sends a transmission to the satellite. This is called a Uplink. The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink. 14

BASICS: ADVANTAGES OF SATELLITES The advantages of satellite communication over terrestrial communication are: The coverage area of a satellite greatly exceeds that of a terrestrial system. § Transmission cost of a satellite is independent of the distance from the center of the coverage area. § Satellite to Satellite communication is very precise. § Higher Bandwidths are available for use. § 15

BASICS: DISADVANTAGES OF SATELLITES The disadvantages of satellite communication: Launching satellites into orbit is costly. § Satellite bandwidth is gradually becoming used up. § There is a larger propagation delay in satellite communication than in terrestrial communication. § 16

BASICS: HOW SATELLITES ARE USED Service Types § Fixed Service Satellites (FSS) • § Broadcast Service Satellites (BSS) • • § Example: Point to Point Communication Example: Satellite Television/Radio Also called Direct Broadcast Service (DBS). Mobile Service Satellites (MSS) • Example: Satellite Phones 17

TYPES OF SATELLITE BASED NETWORKS Based GEO on the Satellite Altitude – Geostationary Orbits 36000 Km = 22300 Miles, equatorial, High latency MEO High bandwidth, High power, High latency LEO – Medium Earth Orbits – Low Earth Orbits Low power, Low latency, More Satellites, Small Footprint VSAT Very Small Aperture Satellites Private WANs 18

SATELLITE ORBITS n n n Geosynchronous Orbit (GEO): 36, 000 km above Earth, includes commercial and military communications satellites, satellites providing early warning of ballistic missile launch. Medium Earth Orbit (MEO): from 5000 to 15000 km, they include navigation satellites (GPS, Galileo, Glonass). Low Earth Orbit (LEO): from 500 to 1000 km above Earth, includes military intelligence satellites, weather satellites. Source: Federation of American Scientists [www. fas. org] 19

SATELLITE ORBITS 20

TYPES OF SATELLITES Satellite Orbits § § § GEO LEO Molniya Orbit HAPs Frequency Bands 21

GEOSTATIONARY EARTH ORBIT (GEO) These satellites are in orbit 35, 863 km above the earth’s surface along the equator. Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth. 22

GEO (CONT. ) Advantages A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface. § GEO satellites have a 24 hour view of a particular area. § These factors make it ideal for satellite broadcast and other multipoint applications. § 23

GEO (CONT. ) Disadvantages A GEO satellite’s distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication. § GEO satellites, centered above the equator, have difficulty broadcasting signals to near polar regions § 24

LOW EARTH ORBIT (LEO) LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1, 500 km above the surface. LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. A network of LEO satellites is necessary for LEO satellites to be useful 25

LEO (CONT. ) Advantages A LEO satellite’s proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication. § A LEO satellite’s smaller area of coverage is less of a waste of bandwidth. § 26

LEO (CONT. ) Disadvantages A network of LEO satellites is needed, which can be costly § LEO satellites have to compensate for Doppler shifts cause by their relative movement. § Atmospheric drag effects LEO satellites, causing gradual orbital deterioration. § 27

MEDIUM EARTH ORBIT (MEO) A MEO satellite is in orbit somewhere between 8, 000 km and 18, 000 km above the earth’s surface. MEO satellites are similar to LEO satellites in functionality. MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. MEO satellites have a larger coverage area than LEO satellites. 28

MEO (CONT. ) Advantage § A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network. Disadvantage § A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite. 29

OTHER ORBITS Molniya Orbit Satellites Used by Russia for decades. § Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours. § A series of three Molniya satellites can act like a GEO satellite. § Useful in near polar regions. § 30

OTHER ORBITS (CONT. ) High Altitude Platform (HAP) One of the newest ideas in satellite communication. § A blimp or plane around 20 km above the earth’s surface is used as a satellite. § HAPs would have very small coverage area, but would have a comparatively strong signal. § Cheaper to put in position, but would require a lot of them in a network. § 31

FREQUENCY BANDS Different kinds of satellites use different frequency bands. § § § § L–Band: 1 to 2 GHz, used by MSS S-Band: 2 to 4 GHz, used by MSS, NASA, deep space research C-Band: 4 to 8 GHz, used by FSS X-Band: 8 to 12. 5 GHz, used by FSS and in terrestrial imaging, ex: military and meteorological satellites Ku-Band: 12. 5 to 18 GHz: used by FSS and BSS (DBS) K-Band: 18 to 26. 5 GHz: used by FSS and BSS Ka-Band: 26. 5 to 40 GHz: used by FSS 32

CAPACITY ALLOCATION FDMA FAMA-FDMA § DAMA-FDMA § TDMA § Advantages over FDMA 33

FDMA Satellite frequency is already broken into bands, and is broken in to smaller channels in Frequency Division Multiple Access (FDMA). Overall bandwidth within a frequency band is increased due to frequency reuse (a frequency is used by two carriers with orthogonal polarization). 34

FDMA (CONT. ) The number of sub-channels is limited by three factors: Thermal noise (too weak a signal will be effected by background noise). § Intermodulation noise (too strong a signal will cause noise). § Crosstalk (cause by excessive frequency reusing). § 35

FDMA (CONT. ) FDMA can be performed in two ways: Fixed-assignment multiple access (FAMA): The subchannel assignments are of a fixed allotment. Ideal for broadcast satellite communication. § Demand-assignment multiple access (DAMA): The subchannel allotment changes based on demand. Ideal for point to point communication. § 36

TDMA (Time Division Multiple Access) breaks a transmission into multiple time slots, each one dedicated to a different transmitter. TDMA is increasingly becoming more widespread in satellite communication. TDMA uses the same techniques (FAMA and DAMA) as FDMA does. 37

TDMA (CONT. ) Advantages of TDMA over FDMA. Digital equipment used in time division multiplexing is increasingly becoming cheaper. § There advantages in digital transmission techniques. Ex: error correction. § Lack of intermodulation noise means increased efficiency. § 38

FREQUENCY BAND TRADE-OFFS The use of letters probably dates back to World War II as a form of shorthand simple code for developers of early microwave hardware. Two band designation systems are in use: adjectival (meaning the bands are identified by the following adjectives) and letter (which are codes to distinguish bands commonly used in space communications and radar). 39

FREQUENCY BAND TRADE-OFFS Adjectival band designations, frequency in Gigahertz: Very high frequency (VHF): 0. 03– 0. 3; Ultra high frequency (UHF): 0. 3– 3; Super high frequency (SHF): 3– 30; Extremely high frequency (EHF): 30– 300. 40

FREQUENCY BAND TRADE-OFFS Letter band designations, frequency in Gigahertz: L: 1. 0– 2. 0; S: 2. 0– 4. 0; C: 4. 0– 8. 0; X: 8– 12; Ku: 12– 18; Ka: 18– 40; Q: 40– 60; V: 60– 75; W: 75– 110. 41

FREQUENCY BAND TRADE-OFFS Today, the letter designations continue to be the popular buzzwords that identify band segments that have commercial application in satellite communications. The international regulatory process, maintained by the ITU, does not consider these letters but rather uses band allocations and service descriptors listed next and in the right-hand column of Figure 2. 9. 42

FREQUENCY BAND TRADE-OFFS Fixed Satellite Service (FSS): between Earth stations at given positions, when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-tosatellite links, which may also be operated in the inter-satellite service; the FSS may also include feeder links for other services. Mobile Satellite Service (MSS): between mobile Earth stations and one or more space stations (including multiple satellites using inter-satellite links). This service may also include feeder links necessary for its operation. Broadcasting Satellite Service (BSS): A service in which signals transmitted or retransmitted by space stations are intended for direct reception by the general public. In the BSS, the term “direct reception” shall encompass both individual reception and community reception. Inter-satellite Link (ISL): A service providing links between satellites. 43

FREQUENCY BAND TRADE-OFFS The lower the band in frequency, the better the propagation characteristics. This is countered by the second general principle, which is that the higher the band, the more bandwidth that is available. The MSS is allocated to the L - and S-bands, where propagation is most forgiving. Yet, the bandwidth available between 1 and 2. 5 GHz, where MSS applications are authorized, must be shared not only among GEO and non. GEO applications, but with all kinds of mobile radio, fixed wireless, broadcast, and point-to-point services as well. The competition is keen for this spectrum due to its excellent space and terrestrial propagation characteristics. The rollout of wireless services like cellular radiotelephone, PCS, wireless LANs, and 3 G may conflict with advancing GEO and non-GEO MSS systems. Generally, government users in North America and Europe, particularly in the military services, have employed selected bands such as S, X, and Ka to isolate themselves from commercial applications. However, this segregation has disappeared as government users discover the features and attractive prices that commercial systems may offer. 44

FREQUENCY BAND TRADE-OFFS On the other hand, wideband services like DTH and broadband data services can be accommodated at frequencies above 3 GHz, where there is more than 10 times the bandwidth available. Add to this the benefit of using directional ground antennas that effectively multiply the unusable number of orbit positions. Some wideband services have begun their migration from the wellestablished world of C-band to Ku- and Ka-bands. Higher satellite EIRP used at Ku-band allows the use of relatively small Earth station antennas. On the other hand, C-band should maintain its strength for video distribution to cable systems and TV stations, particularly because of the favorable propagation environment, extensive global coverage, and legacy investment in Cband antennas and electronic equipment. 45

ULTRA HIGH FREQUENCY While the standard definition of UHF is the range of 300 to 3, 000 MHz (0. 3 to 3 GHz), the custom is to relate this band to any effective satellite communication below 1 GHz. Frequencies above 1 GHz are considered later on. The fact that the ionosphere provides a high degree of attenuation below 100 MHz makes this at the low end of acceptability (the blockage by the ionosphere at 10 MHz goes along with its ability to reflect radio waves, a benefit for ground-to-ground air-to-ground communications using what is termed sky wave or “skip”). UHF satellites employ circular polarization (CP) to avoid Faraday effect, wherein the ionosphere rotates any linear-polarized wave. The UHF spectrum between 300 MHz and 1 GHz is exceedingly crowded on the ground and in the air because of numerous commercial, government, and other civil applications. Principal among them is television broadcasting in the VHF and UHF bands, FM radio, and cellular radio telephone. However, we cannot forget less obvious uses like vehicular and handheld radios used by police officers, firefighters, amateurs, the military, taxis and other commercial users, and a variety of unlicensed applications in the home. 46

ULTRA HIGH FREQUENCY From a space perspective, the dominant space users are military and space research (e. g. , NASA in the United States and ESA in Europe). These are all narrow bandwidth services for voice and low-speed data transfer in the range of a few thousand hertz or, equivalently, a few kilobytes per second. From a military perspective, the first satellite to provide narrowband voice services was Tacsat. This experimental bird proved that a GEO satellite provides an effective communications service to a mobile radio set that could be transported on a person’s back, installed in a vehicle, or operated from an aircraft. Subsequently, the U. S. Navy procured the Fleetsat series of satellites from TRW, a very successful program in operational terms. This was followed by Leasat from Hughes, and currently the UHF Follow-On Satellites from the same maker (now Boeing Satellite Systems). 47

ULTRA HIGH FREQUENCY From a commercial perspective, the only VHF project that one can identify is Orb. Comm, a low data rate LEO satellite constellation developed by Orbital Sciences Corporation. Orb. Comm provides a near-real-time messaging service to inexpensive handheld devices about the size of a small transistor radio. On the other hand, its more successful use is to provide occasional data transmissions to and from moving vehicles and aircraft. Due to the limited power of the Orb. Comm satellites (done to minimize complexity and investment cost), voice service is not supported. Like other LEO systems, Orb. Comm as a business went into bankruptcy; it may continue in another form as the satellites are expected to keep operating for some time. 48

SATELLITE TRANSMISSION BANDS Frequency Band C Downlink Uplink 3, 700 -4, 200 MHz 5, 925 -6, 425 MHz Ku 11. 7 -12. 2 GHz 14. 0 -14. 5 GHz Ka 17. 7 -21. 2 GHz 27. 5 -31. 0 GHz The C band is the most frequently used. The Ka and Ku bands are reserved exclusively 49 for satellite communication but are subject to rain attenuation

L-BAND Frequencies between 1 and 2 GHz are usually referred to as L-band, a segment not applied to commercial satellite communication until the late 1970 s. Within this 1 GHz of total spectrum, only 30 MHz of uplink and downlink, each, was initially allocated by the ITU to the MSS. The first to apply L-band was COMSAT with their Marisat satellites. Constructed primarily to solve a vital need for UHF communications by the U. S. Navy, Marisat also carried an L-band transponder for early adoption by the commercial maritime industry. COMSAT took a gamble that MSS would be accepted by commercial vessels, which at that time relied on high frequency radio and the Morse code. Over the ensuing years, Marisat and its successors from Inmarsat proved that satellite communications, in general, and MSS, in particular, are reliable and effective. By 1993, the last commercial HF station was closed down. With the reorganization and privatization of Inmarsat, the critical safety aspects of the original MSS network are being transferred to a different operating group. 50

L-BAND Early MSS Earth stations required 1 -m dish antennas that had to be pointed toward the satellite. The equipment was quite large, complex, and expensive. Real demand for this spectrum began to appear as portable, land-based terminals were developed and supported by the network. Moving from rack-mounted to suitcase-sized to attaché case and finally handheld terminals, the MSS has reached consumers. 51

L-BAND The most convenient L-band ground antennas are small and ideally do not require pointing toward the satellite. We are all familiar with the very simple cellular whip antennas used on cars and handheld mobile phones. Common L-band antennas for use with Inmarsat are not quite so simple because there is a requirement to provide some antenna gain in the direction of the satellite so a coarse pointing is needed. Additional complexity results from a dependence on circular polarization to allow the mobile antenna to be aligned along any axis (and to allow for Faraday rotation). First generation L-band rod or mast antennas are approximately 1 m in length and 2 cm in diameter. This is to accommodate the long wire coil that is contained within. The antenna for the handheld phone is more like a fat fountain pen. 52

L-BAND While there is effectively no rain attenuation at L-band, the ionosphere does introduce a source of significant link degradation. This is in the form of rapid fading called ionospheric scintillation, which is the result of the RF signal being split into two parts: The direct path and a refracted (or bent) path. At the receiving station, the two signals combine with random phase sometime resulting in the cancellation of signals, producing a deep fade. Ionospheric scintillation is most pronounced in equatorial regions and around the equinoxes (March and September). Both ionospheric scintillation and Faraday rotation decrease as frequency increases and are nearly negligible at Ku-band higher. Transmissions at UHF are potentially more seriously impaired and for that reason, and additional fade margin over and above that at Lband may be required. 53

L-BAND From an overall standpoint, L-band represents a regulatory challenge but not a technical one. There are more users and uses for this spectrum than there is spectrum to use. Over time, technology will improve spectrum efficiency. Techniques like digital speech compression and bandwidth efficient modulation may improve the utilization of this very attractive piece of spectrum. The business failure of LEO systems like Iridium and Globalstar had raised some doubts that L-band spectrum could be increased. One could argue that more profitable land-based mobile radio services (e. g. , cellular and wireless data services) could end up winning over some of the L-band. This will require never-ending vigilance from the satellite community. 54

S-BAND S-band was adopted early for space communications by NASA and other governmental space research activities around the world. It has an inherently low background noise level and suffers less from ionospheric effects than L-band. DTH systems at S-band were operated in past years for experiments by NASA and as operational services by the Indian Space Research Organization and in Indonesia. More recently, the ITU allocated a segment of S-band for MSS and Digital Audio Radio (DAR) broadcasting. These applications hold the greatest prospect for expanded commercial use on a global basis. 55

S-BAND As a result of a spectrum auction, two companies were granted licenses by the FCC and subsequently went into service in 2001– 2002. S-band spectrum in the range of 2, 320 to 2, 345 MHz is shared equally between the current operators, XM Radio and Sirius Satellite Radio. A matching uplink to the operating satellites was assigned in the 7, 025 - to 7, 075 -MHz bands. Both operators installed terrestrial repeaters that fill dead spots within urban areas. With an EIRP of nominally 68 d. BW, these broadcast satellites can deliver compressed digital audio to vehicular terminals with low gain antennas. 56

S-BAND As a higher frequency band than L-band, it will suffer from somewhat greater (although still low) atmospheric loss and less ability to adapt to local terrain. LEO and MEO satellites are probably a good match to S-band since the path loss is inherently less than for GEO satellites. One can always compensate with greater power on the satellite, a technique used very effectively at Ku-band. 57

C-BAND Once viewed as obsolete, C-band remains the most heavily developed and used piece of the satellite spectrum. During recent World Radio-communication Conferences, the ITU increased the available uplink and downlink bandwidth from the original allocation of 500 to 800 MHz. This spectrum is effectively multiplied by a factor of two with dual polarization. Further reuse by a factor of between two and five takes advantage of the geographic separation of land coverage areas. The total usable C-band spectrum bandwidth is therefore in the range of 568 GHz to 1. 44 THz, which compares well with land-based fiber optic systems. The added benefit of this bandwidth is that it can be delivered across an entire country or ocean region. 58

C-BAND Even though this represents a lot of capacity, there are situations in certain regions where additional satellites are not easily accommodated. In North America, there are more than 35 C-band satellites in operation across a 70° orbital arc. This is the environment that led the FCC in 1985 to adopt the radical (but necessary) policy of 2° spacing. The GEO orbit segments in Western Europe and east Asia are becoming just as crowded as more countries launch satellites. European governments mandated the use of Ku-band for domestic satellite communications, delaying somewhat the day of reckoning. Asian and African countries favor C-band because of reduced rain attenuation as compared to Ku- and Ka-bands, making Cband slots a vital issue in that region. 59

C-BAND C-band is a good compromise between radio propagation characteristics and available bandwidth. Service characteristics are excellent because of the modest amount of fading from rain and ionospheric scintillation. The one drawback is the somewhat large size of Earth station antenna that must be employed. The 2° spacing environment demands antenna diameters greater than 1 m, and in fact 2. 4 m is more the norm. This size is also driven by the relatively low power of the satellite, itself the result of sharing with terrestrial microwave. High-power video carriers must generally be uplinked through antennas of between 7 m and 13 m; this assures an adequate signal and reduces the radiation into adjacent satellites and terrestrial receivers. 60

C-BAND The prospects for C-band are good because of the rapid introduction of digital compression for video transmission. New C-band satellites with higher EIRP, more transponders, and better coverage are giving C-band new life in the wide expanse of developing regions such as Africa, Asia, and the Pacific. 61

X-BAND Government and military users of satellite communication established their fixed applications at X-band. This is more by practice than international rule, as the ITU frequency allocations only indicate that the 8 -GHz portion of the spectrum is designated for the FSS regardless of who operates the satellite. From a practical standpoint, X-band can provide service quality at par with C-band; however, commercial users will find equipment costs to be substantially higher due to the thinner market. Also, military-type Earth stations are inherently expensive due to the need for rugged design and secure operation. Some countries have filed for X-band as an expansion band, hoping to exploit it for commercial applications like VSAT networks and DTH services. As discussed previously, S-DARS in the United States employs X-band feeder uplinks. On the other hand, military usage still dominates for many fixed and mobile applications. 62

KU-BAND Ku-band spectrum allocations are somewhat more plentiful than Cband, comprising 750 MHz for FSS and another 800 MHz for the BSS. Again, we can use dual polarization and satellites positions 2° apart. Closer spacings are not feasible because users prefer to install yet smaller antennas, which have the same or wider beam-width than the correspondingly larger antennas for C-band service. Typically implemented by different satellites covering different regions, Ku regional shaped spot beams with geographic separation allow up to approximately 10 X frequency reuse. This has the added benefit of elevating EIRP using modest transmit power; G/T likewise increases due to the use of spot beams. The maximum available Ku-band spectrum could therefore amount to more than 4 THz. 63

KU-BAND Exploiting the lack of frequency sharing and the application of higher power in space, digital DTH services from DIRECTV and Echo. Star in North America ushered in the age of low-cost and userfriendly home satellite TV. The United Kingdom, continental Western Europe, Japan, and a variety of other Asian countries likewise enjoy the benefits of satellite DTH. As a result of these developments, Ku-band has become a household fixture (if not a household word). 64

KU-BAND The more progressive regulations at Ku-band also favor its use for two-way interactive services like voice and data communication. Low-cost VSAT networks typify this exploitation of the band the regulations. Being above C-band, the Ku-band VSATs and DTH receivers must anticipate more rain attenuation. A decrease in capacity can be countered by increasing satellite EIRP. Also, improvements on modulation and forward error correction are making terminals smaller and more affordable for a wider range of uses. Thin route applications for telephony and data, benefit from the lack of terrestrial microwave radios, allowing VSATs to be placed in urban and suburban sites. 65

KA-BAND Ka-band spectrum is relatively abundant and therefore attractive for services that cannot find room at the lower frequencies. There is 2 GHz of uplink and downlink spectrum available on a worldwide basis. Conversely, with enough downlink EIRP, smaller antennas will still be compatible with 2° spacing. Another facet of Ka-band is that small spot beams can be generated onboard the satellite with achievable antenna apertures. The design of the satellite repeater is somewhat more complex in this band because of the need for cross connection and routing of information between beams. Consequently, there is considerable interest in the use of onboard processing to provide a degree of flexibility in matching satellite resources to network demands. 66

KA-BAND The Ka-band region of the spectrum is perhaps the last to be exploited for commercial satellite communications. Research organizations in the United States, Western Europe, and Japan have spent significant sums of money on experimental satellites and network application tests. 67

KA-BAND From a technical standpoint, Ka-band has many challenges, the biggest being the much greater attenuation for a given amount of rainfall (nominally by a factor of three to four, in decibel terms, for the same availability). This can, of course, be overcome by increasing the transmitted power or receiver sensitivity (e. g. , antenna diameter) to gain link margin. Some other techniques that could be applied in addition to or in place of these include: (1) dynamic power control on the uplink and downlink, (2) reducing the data rate during rainfall, (3) transferring the transmission to a lower frequency such as Ku- or C-bands, and (4) using multiple-site diversity to sidestep heavy rain-cells. Consideration of Ka-band for an application will involve finding the most optimum combination of these techniques. 68

KA-BAND The popularity of broadband access to the Internet through DSL and cable modems has encouraged several organizations to consider Ka-band as an effective means to reach the individual subscriber. Ultra-small aperture terminals (USATs) capable of providing two-way highspeed data, in the range of 384 Kbps to 20 Mbps, are entirely feasible at Kaband. Hughes Electronics filed with the FCC in 1993 for a two-satellite system called Spaceway that would support such low-cost terminals. In 1994, they extended this application to include up to an additional 15 satellites to extend the service worldwide. The timetable for Spaceway has been delayed several times since its intended introduction in 1999. While this sounds amazing, strong support from Craig Mc. Caw, founder of Mc. Caw Cellular (now part of AT&T Wireless), and Bill Gates (cofounder of Microsoft) lent apparent credibility to Teledesic. In 2001, Teledesic delayed introduction of the Ka-band LEO system. A further development occurred in 2003 when Craig Mc. Caw bought a controlling interest in L/S-band non-GEO Globalstar system. 69

KA-BAND While the commercial segment has taken a breather on Kaband, the same cannot be said of military users. The U. S. Navy installed a Ka-band repeater on some of their UHF Follow-On Satellites to provide a digital broadcast akin to the commercial DTH services at Ku-band. It is known as the Global Broadcast Service (GBS) and provides a broadband delivery system for video and other content to ships and land-based terminals. In 2001, the U. S. Air Force purchased three X- and Ka-band satellites from Boeing Satellite Systems. These will expand the Ka-band capacity by about three on a global basis, in time to support a growth in the quantity and quality of Ka-band military terminals. The armed services, therefore, are providing the proving grounds for extensive use of this piece of the satellite spectrum. 70

Q AND V-BANDS Frequencies above 30 GHz are still considered to be experimental in nature, and as yet no organization has seen fit to exploit this region. This is because of the yet more intense rain attenuation and even atmospheric absorption that can be experienced on space-ground paths. Q- and V-bands are also a challenge in terms of the active and passive electronics onboard the satellite and within Earth stations. Dimensions are extremely small, amplifier efficiencies are low, and everything is more expensive to build and test. For these reasons, few have ventured into the regime, which is likely to be the story for some time. Perhaps one promising application is for ISLs, also called cross links, to connect GEO and possibly non-GEO satellites to each other. To date, the only commercial application of ISLs is for the Iridium system, and these employ Ka-band. 71

ADVANTAGES OF SATELLITE COMMUNICATION Can reach over large geographical area Flexible (if transparent transponders) Easy to install new circuits Circuit costs independent of distance Broadcast possibilities Temporary applications (restoration) Niche applications Mobile applications (especially "fill-in") Terrestrial network "by-pass" Provision of service to remote or underdeveloped areas User has control over own network 1 -for-N multipoint standby possibilities 72

DISADVANTAGES OF SATELLITE COMMUNICATION Large up front capital costs (space segment and launch) Terrestrial break even distance expanding (now approx. size of Europe) Interference and propagation delay Congestion of frequencies and orbits 73

WHEN TO USE SATELLITES When the unique features of satellite communications make it attractive When the costs are lower than terrestrial routing When it is the only solution Examples: Communications to ships and aircraft (especially safety communications) TV services - contribution links, direct to cable head, direct to home Data services - private networks Overload traffic Delaying terrestrial investments 1 for N diversity Special events 74

REFERENCE BOOKS Title: The Satellite Communication Applications Handbook Author: Bruce R. Elbert ISBN: 1580534902 EAN: 9781580534901 Publisher: Artech House Publishers 75

REFERENCE BOOKS Title: Satellite Communications Author: Dennis Roddy ISBN: 0071371761 EAN: 9780071371766 Publisher: Mc. Graw-Hill Professional 76

REFERENCE BOOKS Title: Satellite Communication Engineering Author: Michael O. Kolawole ISBN: 082470777 X EAN: 9780071371766 Publisher: Marcel Dekker, Inc. 77

QUESTIONS/COMMENTS? 78